Equilibrium dialysis is a procedure for measuring the concentration of free, relatively small molecules in a sample. Dialysis is a separation process for substances in solution driven by a concentration gradient and utilizing their varying diffusion rates through a semi-permeable membrane. Dialysis is employed to retain large molecule while allowing the passage of small ones.
U.S. Pat. No. 6,776,908 discloses a micro-equilibrium dialysis vertically-loaded apparatus. This document states that historically, equilibrium dialysis applications, such as binding and affinity studies, have been slow, difficult and costly to perform. One of the best currently available devices for equilibrium dialysis, for example, only allows for a maximum of twenty samples to be tested simultaneously per device and requires expensive equipment which is often difficult to use and timely to assemble. The device also is not adaptable to standard 96-well pipetting equipment nor does it easily lend itself to automation through the use of robotic systems. Further, this document discloses that this currently available device utilizes oval or circular dialysis membranes which are placed on top of a hemi-spherical or cylindrical lower half of the testing cell and over which is joined the corresponding top half of the cell. The samples are inserted into the cells using a syringe with a blunt nose needle. Up to five cells can be stacked together and once assembled and filled, the stack is rotated continuously on the axis perpendicular to the dialysis membranes on a spit-like mechanism. Four rows of cells can be placed on top of one another in the dialyzer such that a maximum of twenty cells can be utilized at one time. One problem with this spatial orientation is that it requires continuous rotation of the cells so that the samples remain in constant contact with the dialysis membrane so as to avoid concentration polarization. Another problem is that air bubbles which become trapped against the dialysis membrane slow down or prohibit dialysis. To solves these problems, U.S. Pat. No. 6,776,908 provides an equilibrium dialysis device comprising a body, comprising a surface having a first plane and a bottom surface having a second plane, the body is containing ninety-six wells arranged in an 8×12 array. Each of the wells is separated into a first side and a second side, by means for vertically separating the well, such that both sides of each well are fully open and accessible from the top surface of the body and closed on the bottom surface, wherein the body of the device comprises the material polytetrafluoroethylene, and wherein the means for vertically separating the well include dialysis membranes.
More particularly, this document details a multi-well dialysis plate designed to be reusable. The concept utilizes 8 strips of membrane that are sandwiched between Teflon® plates, which form the 96 well array, and sealed by clamp compression. There are several problems with this design. Notably there exists the potential for cross talk between the 12-wells associated with each strip. In other words, fluid can migrate from adjacent well to adjacent well by capillary action of the membrane. The design relies on compression of the Teflon® to seal off each well. Since Teflon® is relatively soft, it is conceivable that the wells furthest from the clamping rods will have the least amount of seal compression.